1. Field of the Invention
The present invention relates to a composite material for sliding parts such as pulleys, retainers, sliding parts housings and friction members, and for sliding parts of electric armatures, such as commutator brushes.
2. Description of the Related Art
Conventionally, sliding parts such as pulleys, retainers, housings and friction members are made of resin. Resin is lightweight and easy to work, allowing inexpensive manufacture.
Resin, on the other hand, is inferior in heat resistance, wear resistance, strength and heat conductivity. Therefore, sliding parts made of resin have a short lifetime.
To avoid these drawbacks, a resin mixed with a metal powder is used. Metal is superior to resin in heat resistance, wear resistance, strength and heat conductivity. The mixing of a metal powder in a resin is intended to impart these characteristic properties of metal to the mixture.
The mixture, however, is heavy because a great amount of metal powder must be added to a resin to avoid the above drawbacks.
Conventional electric armature brushes are mostly composed of a metal powder (predominantly of Cu) for providing electric conductivity, graphite for lubrication, and a binder. Among these components, the metal powder mostly has an adverse effect on wear resistance, and therefore, is preferably present in as small an amount as possible, though it is necessary to provide good electric conductivity.
The metal is mostly used in the form of a powder (such as electrolytic powders, atomized powders, and flake powders) in order for the metal to disperse well over the mixture. The metal powder, however, is present as discrete particles in the mixture and causes the mixture to be less conductive than expected from the metal amount contained in the mixture, so that an undesirably great amount of metal powder is unavoidably added in the mixture to ensure good conductivity, even though the lifetime (wear resistance) is reduced. Thus, the conventional electric armature brush has a poor resistance to wearing, because of a great amount of metal powder contained therein.